1. Field of the Invention
The present invention relates to a dielectric barrier discharge lamp, particularly to a dielectric barrier discharge lamp with which the position of a generated streamer of discharge plasma is fixed.
2. Description of the Prior Art
Up to now, this type of dielectric barrier discharge lamp has been used as an ultraviolet light source for exciting a fluorescent material so as to fluoresce, etc. in various fields of technology. For the dielectric barrier discharge lamp, a variety of techniques have been proposed up to now which intend to provide an increased luminance of output light, elimination of the variation in luminance in the radiation area, stabilization to suppress the deterioration of the luminance with time, a higher efficiency to increase the total quantity of radiation per unit input power, an extended service life, simplification of the construction, facilitation of the manufacture, reduction in cost, etc. by generating a number of almost uniformly distributed thin streamers of discharge plasma in the space across the discharge electrodes, which are said to be characteristic of the dielectric barrier discharge lamp.
An embodiment of prior art as given in Japanese Unexamined Patent Publication No. 6 (1994) 231733 (called a first embodiment of prior art) provides a dielectric barrier discharge lamp with which the discharge container is filled with a discharge gas to form excimer molecules by dielectric barrier discharge, and a window member to take out the light radiated from the excimer molecules generated by the dielectric barrier discharge is provided. For this first embodiment of prior art, it is proposed that the content of OH group in the silica glass used for the window member should be decreased to under 10 ppm by weight. Generally, with dielectric barrier discharge lamps, the silica glass used as the window member to take out the light to the outside of the discharge container is deteriorated, being eroded by the halogen with the lapse of on-time. For this first embodiment of prior art, it is stated that, by restricting the amount of OH group contained in the silica glass, the erosion of the silica glass by the halogen is suppressed, therefore the reduction in output light intensity resulting from the erosion is suppressed, and the decrease in density of the excimer molecules containing halogen can be prevented.
For a dielectric barrier discharge lamp according to an embodiment of prior art as proposed in Japanese Unexamined Patent Publication No. 6 (1994)-310102 (called a second embodiment of prior art), it is stated that, by configuring one of the opposed electrodes as a conductive net; specifying the thickness of the conductive wires constituting the conductive net for the electrode provided in the light-permeable dielectric in the window opening to take out light to be 0.2 mm or less; and specifying the area of one mesh in the conductive net to be a value between 0.04 and 2.5 mm2, the radiation output efficiency can be improved and the light output can be stabilized.
However, generally, with dielectric barrier discharge lamps, when they are in radiation, the thin streamers of discharge plasma generated in the space across the discharge electrodes constantly move at a low speed, and if the luminance is measured at a given point in the window (made of silica glass) in the discharge container, the luminance offers a xe2x80x9cfluctuationxe2x80x9d with time. With conventional dielectric barrier discharge lamps, this xe2x80x9cfluctuationxe2x80x9d has been an essential problem which cannot be avoided. In addition, to generate more thin streamers at discharge plasma in the space across the discharge electrodes stably, the material, the construction, etc. of the dielectric barrier discharge lamp must meet more requirements, which presents a problem of that meeting the requirements increases the manufacturing cost. For the above-stated conventional dielectric barrier discharge lamps, solutions to these problems have not always been clearly indicated.
The above-stated conventional dielectric barrier discharge lamps have a disadvantage of that the movement of the streamers in radiation output causes the luminance in the light output window to have a xe2x80x9cfluctuationxe2x80x9d with time, and this xe2x80x9cfluctuationxe2x80x9d of the luminance cannot be prevented. In addition, if more streamers are to be generated stably in order to lower the degree of xe2x80x9cfluctuationxe2x80x9d of the luminance, the number of requirements to be met by the material and the construction is increased, and with this increase in the number of requirements, the manufacturing cost is inevitably increased.
The present invention offers the following means to solve the above-stated problems.
(1) A dielectric barrier discharge lamp comprising a cylindrical discharge container which permeates ultraviolet radiation, a discharge gas sealed in the discharge container, and a pair of discharge electrodes provided at the outside surface of the discharge container with the end portions being in contact with it, in which the end portions of two discharge electrodes constituting the pair of electrodes are opposed to each other across a discharge spacing; the line connecting the ends of the two electrodes to each other is eccentric from, i.e., offset relative to the axis of the discharge container; and a plane perpendicular to the line joining the electrodes is roughly parallel to the axis of the container.
(2) A dielectric barrier discharge lamp as above, in which a stream of discharge plasma generated across the pair of discharge electrodes takes a shape, when viewed from the direction of the axis which, so that at least in portion, it is bent toward the inside wall of the discharge container.
(3) A dielectric barrier discharge lamp as above, in which a current limiting resistor is inserted in series with the pair of discharge electrodes.
As stated above, by providing a pair of opposed electrodes eccentrically (offset) with respect to the axis of the discharge container, the position of the stream of discharge plasma generated in the discharge container can be stabilized, and thus the xe2x80x9cfluctuationxe2x80x9d of the luminance distribution on the ultraviolet radiation receiving surface can be suppressed.
The purpose of the present invention is to offer a dielectric barrier discharge lamp with which occurring of a xe2x80x9cfluctuationxe2x80x9d of the luminance distribution on the ultraviolet radiation receiving surface can be suppressed, and yet the construction is simple.